Investigating the Role of Reactive Oxygen Species on Antibiotic Tolerance in Pseudomonas aeruginosa

<em>Pseudomonas aeruginosa</em> is the primary infectious agent in the lungs of people with cystic fibrosis. Chronic <em>P. aeruginosa</em> infections exacerbate the existing disease, while treating the bacteria with antibiotics is difficult due to its intrinsic adaptations. For example, <em>P. aeruginosa</em> has been found to display tolerance to antibiotic treatment in addition to its well-defined resistance mechanisms. The objective of this study was to investigate how reactive oxygen species mediate <em>P. aeruginosa</em>&rsquo;s tolerance to antibiotics, as previous studies have illustrated that while reactive oxygen species are traditionally understood to be antibacterial agents, they may in fact improve tolerance. To assess how tolerance is impacted by these treatments, a series of tobramycin killing assays were performed where reactive oxygen species concentration was artificially increased to observe changes in tolerance. Additionally, various genes responsible for reactive oxygen species detoxification were deleted to further understand their roles in this process. This study found promising trends that below a certain threshold, reactive oxygen species serve as a pathway for tolerance upon treatment with tobramycin. However, at excessive concentrations, oxidative stress has a detrimental effect to <em>Pseudomonas aeruginosa</em>&rsquo;s survival. It was observed that deletions of the reactive oxygen species-neutralizing genes, &Delta;<em>katB</em> and &Delta;<em>sodM</em>, increase survival at lower concentrations of paraquat, a prototypical reactive oxygen species generator. Meanwhile, deletion of part of the stringent response mechanism, &Delta;<em>relA</em>, causes decreased survival across paraquat additions. Collectively, these results highlight the role of reactive oxygen species as a mechanism of antibiotic tolerance at manageable concentrations for <em>Pseudomonas aeruginosa</em> before increased concentrations sensitize the bacteria to tobramycin, and encourage further study on other reactive oxygen species-neutralization genes. <strong><br /></strong>